The present invention relates to strapping material. More particularly, the present invention concerns a plastic strap formed with an integrated rib for enhancing the stiffness of the strap. Such a strap is particularly useful for automated strapping machines (or “strappers”).
Strapping machines are in widespread use for securing thin bands of plastic strap around loads. One type of known strapper includes a strapping head and drive mechanism mounted within a frame. Mounted to the frame is a chute through which strapping material is fed. Means generally are provided in the chute for guiding and retaining the strap in the chute so that the strap cannot fall or be pulled inwardly against the load until after a loop of strap has been formed around the load. Such means usually include a strap release system that permits the strap to be released from the chute upon tensioning.
Typically, the chute is larger than the load to be strapped so as to accommodate various load sizes and, thus, such strap guiding and retaining means function to initially maintain the strap in the largest possible loop configuration and, of course, function to permit the strap to be fed around the load without impinging upon or snagging upon the load. Moreover, the chute typically is constructed in a shape and size suitable to surround the load to be strapped, and generally is constructed in a quadrilateral shape, such as a square or a rectangle, with four corners, since most loads to be strapped share the same shape.
Prior art chute designs generally employ modular chute components, which are assembled to form the desired chute size and shape. For square and rectangular chutes, the chutes generally are comprised of horizontal and vertical chute sections, which often are supported by support beams, and connected by four corner assemblies. The chute typically is enclosed by a strap retaining and release means of the type well known in the prior art.
In a typical stationary bottom-seal strapper, the chute is mounted at about a work surface, and the strapping head is mounted to a horizontal portion of the chute, below the work surface. The drive mechanism is also mounted below the work surface, near to the strapping head. The drive mechanism urges or feeds the strap through the strapping head, into and around the chute, until the strap material returns to the strapping head to form a loop around the load. Essentially, the strap is pushed through the chute by the drive mechanism. After the strap loop has been formed, tension is applied to the strap to constrict the strap loop about the load and the overlapping strap ends are secured by conventional means to create a sealed, tensioned loop around the load.
Many such machines are employed in processes that maximize the use of fully automated strapping operations. To this end, machines are configured for automated in-feed and out-feed, such that a load to be strapped is automatically fed into the machine by an in-feed conveyor, the strapping process is carried out, and the strapped load is automatically fed out of the machine by an out-feed conveyor. As such, an improper strapping event, such as a strap short feed, wherein the strap does not create a full loop around the load, can create a “ripple effect” along the entire automated strapping process by forcing the shutdown of an entire strapping line. Thus, it is desirable to ensure that the occurrence of any such improper strapping events is minimized.
One of the primary causes of improper strapping events is a strap short feed. A strap short feed occurs, as discussed above, when the strap does not create a full loop around the load. Strap short feeds may be caused by areas along the strap travel path that snag the leading edge of the strap or otherwise cause the strap to gather or bunch. Such areas include the interface between horizontal and vertical sections of the chute and the interface between the chute and the strapping head.
To help avoid strap short feeds, it is desirable that the strap material exhibit a desirable degree of longitudinal stiffness, such that strap's leading edge remains generally parallel to the direction of travel (for example, the strap does not bow or sag downward to an unacceptable degree when traversing along horizontal portions of the chute) and such that the strap resists twisting, snagging or bunching as the strap travels through the chute. However, most prior art plastic straps exhibit only moderate levels of longitudinal stiffness due to the inherent physical properties of the plastic materials used to form such straps, and the desire to manufacture such straps with minimal thickness and weight.
To achieve desired increased longitudinal stiffness, many prior art plastic straps are formed with increased thickness and, thus, increased weight. However, it would be advantageous to obtain the desired longitudinal stiffness while decreasing the thickness and weight of the strap material. It is also advantageous to provide a strap that does not twist or take a helical-like form as it traverses through the strap chute.
Accordingly, there is a need for a plastic strap with enhanced longitudinal stiffness that resists snagging or bunching during travel around the chute of a strapper. Desirably, such a strap includes at least one integrated, longitudinally disposed rib for enhancing the stiffness of the strap. More desirably, such a strap is formed with side panels that are parallel to the longitudinal plane of the strap such that the strap does not twist. Most desirably, such as strap is formed with decreased relative thickness and weight as compared to prior art plastic straps offering comparable longitudinal stiffness.